1. Field of the Invention
The present invention relates to a receiving apparatus for receiving radio signal that is transmitted from a mobile communication terminal. More particularly, the present invention relates to a receiving apparatus having cooling section that cools receiving unit that performs a predetermined process to the radio signal.
2. Description of the Related Art
Recently, mobile communication terminals such as car phone, mobile phone of PDC (Personal Digital Cellular), or PHS (Personal Handy Phone System), are widely popularized.
These mobile communication terminals transmit and/or receive radio signal with radio base station. The receiving apparatus that is provided as a receiving system of the radio base station, has an antenna section, a receiving unit for performing processes such as amplification of the radio signal that is received in the antenna section, and a receipt processing circuit for performing predetermined signal processes to the radio signal that is, for example, amplified in the receiving unit. The antenna section is provided with a plurality of antennas for diversity, and a plurality of the receiving units and a plurality of receipt processing circuits may be provided, accordingly.
The receiving unit has receipt filter that is provided for removing interference, and amplifier for compensating reduction in noise figure caused by cable loss between the antenna and the receipt processing circuit or distribution loss to the receipt processing circuit. The receiving unit is provided near the antenna. The amplifier is, for example, low noise amplifier (LNA).
On the other hand, in the event that mobile communication terminal is concerned, radio zone covered by one radio base station is divided into a plurality of areas (Each of the areas is referred to as a “sector,” hereinafter.), each of which is provided with antenna section, receiving unit, and receipt processing circuit, and thereby, one radio system is constructed for every sector.
However, noise figure of the receiving unit is limited to about 3 db.
It can be considered that the noise of the receiving unit (in particular, amplifier) can be reduced by cooling the entire receiving unit in a cooler or that the noise figure is improved by about 0.5 db for the entire receiving unit by using a receipt filter that is made from high-temperature super-conductive material.
However, such a cooler is expensive and does not have sufficient reliability. Therefore, if the cooler is used, the receiving apparatus becomes expensive and its reliability decreases. When a radio zone is divided into a plurality of sectors, or when the radio zone corresponds to diversity, the number of the cooler increases accordingly, thereby increasing costs and decreasing the reliability.